1. The Field of Invention
The invention concerns an extrusion device for manufacturing a product based on a rubber mix in the form of a thin strip. The invention more particularly concerns a device for producing a profiled product based on a rubber mix in the form of a very thin strip which can be very wide and can be directly deposited on a form or drum or directly superimposed on another material at the discharge from the device.
2. The Related Art
In the field of manufacturing tire covers, semi-finished products are produced consisting of mixes of rubber which are then connected to each other. According to the temperature of the products and the nature of the rubber mixes which make up the products, difficulties are frequently encountered in making one product adhere to the other during the manufacture of the tire. The solution to this problem used for a long time by manufacturers consisted of applying a rubber solution dissolved in an organic solvent to one of the products. Now, for reasons of environmental protection, it is sought to eliminate the use of such solvents. It is therefore necessary to have recourse to new solutions.
One solution consists of depositing between the two products to be “stuck” together a very fine layer of rubber products having a very high adhesive power, which is often referred to as a “connecting compound”. Such a connecting compound has been used for a long time in the field of retreading to effect the connection between the cured carcass and a new tread.
In order to be able to place such a layer directly at the discharge from the extruder, notably in order to conserve its temperature, its stickiness and other characteristics of the connecting compound, and also from an industrial point of view, it is particularly advantageous to directly manufacture a very thin strip that is coextensive in width with the element to be covered. Thus, for example, for manufacturing a tire to be retreaded, it is desirable to produce a strip with a width identical to that of the cured tire carcass and having a thickness of around a few tenths of a millimeter.
In addition, it is desirable to make tire covers in a fashion which is ever more precise. Such precision in manufacture depends notably on complying with the dimensions of the rubber products, in particular the precision and constancy of thickness and the width of the products, that are assembled to make up the tire cover.
Different categories of apparatus are already known for effecting rubber extrusions. The extruders, which conventionally have one or more extrusion screws opening out onto an accumulation chamber and driving the rubber mix as far as an extrusion orifice, are divided into two categories:                extruders normally referred to as “roller die extruders”, which are characterized by an extrusion plate consisting of the external surface of a roller which cooperates with a fixed wall, and        so-called “flat die extruders”, characterized by an extrusion plate consisting of fixed walls.        
These extruders make it possible to extrude, in great length, a product whose profile is substantially constant with different advantages for each category of extruder. Whatever the category, the width of the extruded strip obtained is limited with respect to the diameter of the extrusion screw or the distance between the centers of the extrusion screws if it is an extruder having multiple extrusion screws. This is because, if the width of the product and, therefore, the width of the extrusion orifice is very great compared with this diameter or distance, there will be supply problems in bringing sufficient mix with a correct delivery rate as far as the plate and also difficulties in retaining the mix in the plate, as well as difficulties in distributing the mix, pressures and delivery rates over the entire width of the extrusion orifice.
These different items of equipment, therefore, make it possible to obtain products of limited width. This width is all the more limited because, for industrial reasons of having machines which are compact, it is sought to limit the size of the extrusion screw or screws.
In order to remedy these problems, French patent document No. 2,294,039 (U.S. Pat. No. 4,028,031) describes an extruder associated with a calender for producing a wide thin strip of product based on rubber mix. The extruder has an extrusion screw which drives the rubber mix into an accumulation chamber, at the discharge of which there are disposed two rollers whose axes are perpendicular to the axis of the extrusion screw and in the gap between which the strip is “profiled”.
Such a device poses, for a broad strip, not insignificant technical difficulties which can have an effect on the quality of the product. This is because the size of the extrusion orifice is very far away from the final width of the product, which causes a problem in driving the rubber compound and irregular distribution over a much wider surface, in the same way as what was explained above for an extrusion plate with a size very much greater than the diameter of the extrusion screw. It also gives rise to risks of having a production width which is not constant.
In addition, such a device is very bulky since it requires considerable lateral space in the direction of the width of the strip to make it possible to obtain such a width, and an axial dimension, in the direction of the extrusion screw, which is also great.
The invention aims to mitigate these drawbacks.
Hereinafter, “axial”, “radial” and “circumferential” will designate the directions parallel respectively to the axial, radial and circumferential directions with respect to the roller of the extrusion device.